A new type of device could keep your wearables charged via ambient motions.

Ask anyone who uses wearable tech like the Apple Watch what their biggest complaint is and they’ll likely respond: the battery life.

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It’s hard for any moderately advanced wearable—think something with a power-hungry display and Wi-Fi and GPS capabilities—to last longer than 24 hours due to the constraints of today’s battery technology. This battery life drawback is why so many think wearables will only truly become mainstream when we can put the annoyance of having to plug them in on a daily basis behind us.

But the days of less than day-long wearable battery life could be coming to an end thanks to a new type of bending “battery” technology developed at MIT. A team of researchers led by professor Ju Li have developed a non-mechanical method of generating energy by the subtle bending of two sheets of lithium alloys separated by a liquid electrolyte. When the alloys are bent from small ambient motions—such as what happens when you walk or reach for that pen on your desk—the device generates electricity.

If you’re wondering why Li’s device is referred to as a “battery” in quotes, it’s because it technically isn’t one: It doesn’t store any electricity like a traditional batter does. Instead it converts the motion from small bending movements into electricity, which is output right away. Due to this, the device is ideal for wearables since they are always attached to your body, which is making micro bending motions all the time. Such a device could easily be incorporated into the band of an Apple Watch, for example.

Li says the device is currently 15% efficient, but because it isn’t limited by the second law of thermodynamics, which sets maximum limits on theoretically possible efficiencies, the device could eventually be 100% efficient. Li also says the test device currently shows little reduction in performance even after 1,500 cycles of bending.

And it’s not just wearables that this new bending tech can keep powered. “Efficient harvesting of such mechanical energies will help to develop more capable and intelligent wearable devices and human-machine interfaces,” he told MIT News. “This work presents huge potential in many applications such as flexible electronics, self-powered sensors, wearable devices, human-machine interfaces, robotics, artificial skin, etc.”

Of course, Li’s device only exists in the labs at MIT for now, but given the importance that tech companies place on extending battery life in their devices, such a promising technology could be rapidly commercialized if further iterations of it continue to improve.